Sporadic outbreaks of illness resulting from microbial contamination of meat and poultry products are a continuing source of medical and public health concern. Salmonella typhimurium is a frequent contaminant of poultry, causing severe gastroenteritis which is usually brief and limited to the gastrointestinal tract, but can be more severe in children and the aged. S. typhimurium is the most frequently isolated serotype of Salmonella in the United States; however, related serotypes include S. typhi which causes typhoid fever and S. paratyphi which causes a milder disease, paratyphoid fever. E. coli 0157:H7 is another contaminant of livestock that has recently become a serious public health threat. E. coli 0157:H7 causes severe hemorrhagic diarrhea and renal disease which can be fatal. Due to the increased incidence of disease from contaminated meat and poultry products, a need has arisen to augment the standard public health measures of control. Such measures are typically applied during processing and packaging, not during growth and rearing of animals for market.
Biological control of pathogen contamination of birds and animals grown for food has rarely been described. Doyle et al., U.S. Pat. No. 5,302,388 described microorganisms capable of preventing Campylobacter jejuni colonization of poultry. The microorganisms were selected on the basis of their ability to interfere with specific colonization requirements of C. jejuni. Such an approach is not applicable to organisms such as S. typhimurium or E. coli 0157:H7, since these do not necessarily colonize the host animal, but are simply part of the intestinal flora, where they are able to find nutrients and to multiply.
Bacteriocin is a generic term applied to any of a set of proteinaceous antimicrobial agents produced by certain bacterial strains. Colicin is the term specifically applied to certain bacteriocins produced by E. coli. The colicins have been subject to most bacteriocin-related research, although such research has not been extensive. The term microcin has been used in the literature with varying definitions, depending upon the author.
The term microcin is sometimes applied to antibiotic substances produced by diverse strains of Enterobacteriaceae able to pass through dialysis membranes having a molecular weight cut-off of about 10,000 daltons and produced during stationary phase culture. [Moreno, F., et al. (1995) in Biotechnology Series 28, Genetics and Biochemistry of Antibiotics Production, pp.307-321, Butterworth-Heineman Ltd., London]. The bacteriocins have been studied as possible means for strain typing, as possible virulence factors and for the mechanism of their toxicity. The genes for most bacteriocins are carried on plasmids which encode the structural gene, post-translational processing genes and an immunity gene that confers immunity to the cell producing the toxin. There is no clear-cut evidence that production of a bacteriocin confers a selective advantage in the microbial environment. Various assays of natural enterobacterial populations have shown that between 30%-50% are Col.sup.+ (capable of producing a colicin). Many colicins are expressed only in response to induction, the inducing agent being typically a DNA damaging agent such as UV light or mitomycin C. Microcins are usually naturally produced during stationary phase existence. Attempts to use bacteriocins as antibiotics or bacteriocin-producing strains as bio-control agents have generally not been successful. For reviews, see Bacteriocins, Microcins and Lantibiotics, R. James et al. eds., Springer-Verlag, Berlin, 1991; Kolter R. et al. (1992) Ann.Rev. Microbiol. 36:125-144; Pegsley, A. P. (1984) Microbiol. Sci. 1:203-205; Moreno F. et al., supra.
O'Brien et al. (1994) Plasmid 31:288-296 reported characterization of E. coli strain 2424, isolated from a human patient with pyelonephritis. E. coli 2424 was found to produce a previously undescribed colicin, designated colicin 24. Colicin 24 was found to have bactericidal activity on agar plates against various E. coli test strains and against S. typhimurium. The molecular weight, estimated by SDS-PAGE, was approximately 37.2 Kda. The plasmid responsible for production of col 24 was isolated and the essential genes for col 24.sup.+ phenotype were transferred to pBR322 to produce a 29.15 kb plasmid, pGOB34, and to pUC18 to produce two 11.39 kb plasmids, pGOB342 and pGOB420, all of which conferred colicin 24 production on host strains transformed by the respective plasmids. The colicin 24 determinants including host immunity appeared to be located on a 8.7 kb Eco RI fragment.